There is a method of calculating the amount of blood flow such as cerebral blood volume (CBV) by using a modality such as an X-ray computed tomography (CT) system or an angio system (an X-ray imaging apparatus). For example, the CBV is calculated based on the profile of CT values obtained by continuous scanning. For another example, the CBV is calculated by using a non-contrast image acquired before the injection of a contrast agent and a contrast image acquired after the injection. Specifically, an image of blood vessels including capillaries is created by removing non-vascular regions such as bones and soft tissues from the difference between the non-contrast image and the contrast image. The generated image is displayed, for example, as a color map.
This method is used to determine the results of procedure, therapy, or treatment for a subject. However, it may sometimes be required to make a different decision according to the state of the subject before a procedure. Besides, the blood flow velocity or the like may vary according to the psychological and physical condition of the subject who is to undergo a procedure or the like. In this case, even if the amount of blood flow is calculated before or after a predetermined event such as a procedure, it may be difficult to determine whether the calculation result is influenced by the predetermined event such as a procedure. For example, even if the CBV is calculated based on an examination result obtained after the predetermined procedure, a viewer of an image may not determine whether a portion, which appears in the image or the like as a result of measurement, emerges after the procedure. In such a case, for example, an affected part or the like that has already existed before the procedure may be mistaken for a newly developed affected part.